Jervis writes "perhaps the most striking characteristic of the postwar world is just that-it can be called "postwar" because the major powers have not fought each other since 1945. Such a lengthy period of peace among the most powerful states is unprecedented. Almost as unusual is the caution with which each superpower has treated the other". He discusses the change in the balance of powers before and after the introduction of nuclear weapons, and the attitudes on the international stage during and after these changes.